Problem: $ D = \left[\begin{array}{rrr}0 & 2 & 2 \\ 0 & 2 & 1 \\ 2 & 2 & 0\end{array}\right]$ What is $ D^{-1}$ ?
Explanation: $ = \left[\begin{array}{rrr}\frac{1}{2} & -1 & \frac{1}{2} \\ -\frac{1}{2} & 1 & 0 \\ 1 & -1 & 0\end{array}\right]$